It is well known that orthogonal frequency division multiplexed (OFDM) systems divide a channel bandwidth into several narrowband subcarriers. Many modern OFDM system proposals include the capability to support frequency-selective resource allocation. During frequency-selective resource allocation, the channel bandwidth is divided into several sub-bands, which may be called tiles or resource blocks. Each resource block includes several adjacent OFDM subcarriers and may span multiple OFDM symbol periods. For example, a resource block in an OFDM system with a 15 kHz subcarrier spacing and a 4.76 us cyclic prefix length could be defined as containing 12 adjacent subcarriers (˜180 kHz) by seven OFDM symbol periods (˜0.5 msec).
The use of resource blocks enables data allocation to a particular user to be made on the resource block having the best channel quality. However, this requires the user to feed back information to identify the best resource block. At high speeds, the channel can change drastically between the time of the feedback report and the time of the data allocation and transmission, leading to poor performance. An alternative to frequency selective allocation is to use a resource allocation that is not localized in frequency, in order to provide frequency diversity. Users given such an allocation can be called frequency diversity users. Frequency diversity users are typically given an allocation that spans the entire channel bandwidth (such as one subcarrier out of every resource block) so that when a deep fade does occur, it only affects a portion of the allocation rather than the entire allocation, thus providing frequency diversity.
The frequency multiplexing between frequency selective and frequency diversity users could be greatly simplified if the same resource-block based structure could be used for both types of users. Therefore, a need exists for a method and apparatus for performing resource allocation and transmission that allows both frequency selective and frequency diversity users to use the same resource-block based transmission scheme while still being capable of providing frequency diversity to the frequency diversity users.